Cycle wheel rim and method of manufacture

ABSTRACT

A cycle wheel having a U-shaped radial cross section, with two lateral sidewalls located on opposite sides of a median plane of the rim and each demarcated by an outer surface facing away from the median plane, on the one hand, and a bridge connecting the sidewalls and including an outer surface facing toward the axis of rotation of the wheel, on the other hand. At least one median zone of the outer surface of the bridge, which has a transverse width measured perpendicular to the median plane and greater than 4 mm, is machined over the entire circumference of the rim.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon French Patent Application No. 12/00021, filed Jan. 4, 2012, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is claimed under 35 U.S.C. §119.

BACKGROUND

1. Field of the Invention

The invention relates to a rim for a cycle wheel, and a method for manufacturing such a rim.

2. Background Information

Conventionally, a cycle wheel rim is annular and has a U-shaped radial cross section, with two lateral sidewalls that are generally perpendicular to the axis of rotation of the wheel and a bridge that connects the lateral sidewalls and is oriented so as to be opposite the axis of rotation of the wheel. In the case of a spoked wheel, the spokes are generally fastened to the bridge of the rim.

To manufacture a cycle wheel rim, it is known to make a rectilinear section by extruding or spinning a metal alloy, such as an aluminum alloy, for example, and then bending the section into an annular shape. The ends of the rim are then connected to one another, for example by welding.

It is advantageous to produce a lightweight rim, in order to optimize the performance of the cyclist, while maintaining sufficient rigidity and strength to avoid breakage.

The extrusion process requires minimum wall thicknesses, for the yield stress increases significantly when the thickness decreases and the characteristics of the alloy and the spinning speed increase. Thus, for alloys that are typically used in the manufacture of rims, it is very risky to go below thicknesses of 0.85 mm, as doing so may quickly break the extrusion die.

In addition, the bending of a section causes significant plastic deformations, particularly in the zones that are away from the center of gravity of the cross section. These substantial plastic deformations cause dislocations of the grains of the material which, in turn, can result in a surface finish known as “orange peel,” which is often considered unsightly.

Furthermore, overly thin lateral walls also generate local buckling of the walls of the section during bending, when subject to overly high compressive deformations.

To overcome the aforementioned drawbacks, the document FR-A-2 727 355 proposes to make a rim by extruding a rectilinear section having sufficient thickness to prevent the extrusion from causing defects in the material. The section is then bent, and it does not change and does not buckle due to its thickness. To reduce the weight of the rim, the rim is then immersed in an aggressive chemical bath which attacks the material and decreases its thickness. This manufacturing method is relatively cumbersome to implement and, although the surface finish does become uniform, it remains quite rough.

Similarly, the document U.S. Pat. No. 6,961,999 proposes extruding and bending a sufficiently thick section in order not to cause manufacturing defects. The lateral sidewalls of the rim are then machined to reduce their thickness and to decrease the weight of the rim. The document EP-A-0 579 525 also proposes machining the lateral sidewalls of the rim after extrusion and bending of the section. Reducing the weight of the rim is not optimal because the bridge of the rim retains its initial thickness.

It is also known, from the documents EP-A-1 084 868 and EP-A-1 491 362, to machine the section after bending, both in the area of the bridge and in the area of the lateral sidewalls of the rim, and only on certain portions of the circumference of the rim. The machining is time-intensive and it is complex to implement, because it requires the use of a five-axis machine.

When it is desired to produce a plurality of rims having various geometries, for example with respect to the number of spokes, the location of the spoke fastening zones, or the thickness of the rim, all of these methods require a modification of the manufacturing parameters, in particular with respect to the machining for material removal and/or chemical milling. This leads to additional development costs and does not standardize the manufacturing method.

SUMMARY

The foregoing are drawbacks that the present invention overcomes, particularly by providing a cycle wheel rim and a method for manufacturing such a rim, which makes it possible to reduce the weight of the rim while optimizing rigidity. In addition, the rim according to the invention can be manufactured quickly, and the manufacturing method prevents the occurrence of defects during the extrusion and bending of the section.

The useful life of rims is often limited by the appearance of cracks in the spoke fastening zone. Once they occur, such cracks propagate very quickly in the spinning direction, quickly causing a rupture of the bridge. This well-known fatigue phenomenon is due to the numerous load cycles to which the spokes are subjected at each turn of the wheel, on the one hand, and it is also accelerated by small surface defects which typically are longitudinal striations caused by friction of the metal in the die during the spinning operation, on the other hand. The invention therefore also optimizes the fatigue strength of the rim by locally reinforcing the fastening of the spoke, but also by improving the surface finish in order to eliminate or delay the initiation of fatigue cracks.

To these ends, the invention provides a cycle wheel rim and a wheel having a U-shaped radial cross section, with two lateral sidewalls located on opposite sides of a median plane of the rim and each demarcated by an outer surface facing away from the median plane, on the one hand, and a bridge connecting the sidewalls and comprising an outer surface facing toward an axis rotation of the wheel, on the other hand. At least one median zone of the outer surface of the bridge, having a transverse width measured perpendicular to the median plane and greater than 4 mm, is machined on at least 95% of the circumference of the rim.

Due to the invention, the bridge of the rim is machined at least partially on the entire circumference of the rim, including in the area of the spoke fastening zones. Thus, the weight of the rim is reduced. In addition, the machining improves the surface finish of the bridge by eliminating the defects resulting from spinning or bending the section, thereby improving the fatigue strength. In the various embodiments which are described below, the machining is done on the entire circumference of the rim. In other embodiments not described in detail below, which are also encompassed by the invention, the machining is carried out on almost the entire circumference. In this case, at least 95%, or even 97%, of the circumference is machined. This configuration may be selected if it is desired, for example, to produce an unbalance to counterbalance the weight of the splice bar of a sleeved rim and/or of the inflation valve. In a particular embodiment, even in the case in which only 95% of the circumference of the rim is machined, it is necessary to ensure that all of the spoke fastening zones are machined.

According to advantageous but not essential aspects of the invention, such a rim may incorporate one or more of the following characteristics, taken in any technically permissible combination:

-   -   The outer surface of the bridge is machined in its entirety,         over the entire circumference of the rim.     -   The rim has an outer surface facing outward of the rim and         including both the outer surface of the bridge and at least a         portion of the outer surface of the sidewalls, which is         connected to the outer surface of the bridge. The outer surface         of the rim is machined in its entirety over the entire         circumference of the rim.     -   The outer surface of the rim comprises the entire outer surface         of the sidewalls.     -   The rim is divided into a plurality of zones which divide the         circumference of the rim into angular sectors, the zones         including:         -   transmission zones located around the zones of attachment of             the spokes of the wheel; and         -   intermediate zones located between the transmission zones.             In the area of the transmission zones, the thickness of the             bridge, measured in the median plane of the rim, is equal to             a maximum thickness. In the area of the intermediate zones,             the thickness of the bridge is equal to a minimum thickness             that is less than the maximum thickness.     -   The maximum thickness of the bridge is greater than 1.6 mm or,         according to a range of variations, greater than 2 mm.     -   The minimum thickness of the bridge is less than 0.8 mm or, in         other embodiments, less than 0.65 mm.     -   The zones further include transition zones each located between         a transmission zone and an intermediate zone. In the area of the         transition zones, the thickness of the bridge is equal to an         intermediate thickness, which varies progressively between the         minimum thickness and maximum thickness of the bridge.     -   In a radial cross section of the rim, a radius of curvature of         the bridge is less than 15 mm or, in a particular embodiment         range, less than 10 mm.     -   The bridge includes internally threaded cylindrical bushings for         fastening the spokes of the wheel, and the bushings are made         unitary with the rim.     -   The sidewalls each define a planar braking surface, provided to         cooperate with a brake pad. A height of at least one braking         surface, measured radially, is greater in the area of the         transmission zones than in the area of the intermediate zones.

The invention also relates to a method for manufacturing a cycle wheel rim, comprising:

-   -   extruding a rectilinear section, such section comprising two         lateral sidewalls located on opposite sides of a median plane of         the rim and each demarcated by an outer surface facing away from         the median plane, on the one hand, and a bridge connecting the         sidewalls and demarcated by an outer surface facing toward an         axis of rotation of the wheel, on the other hand;     -   bending the section to form at least one hoop, or ring;     -   assembling the ends of the hoop formed from the section by         affixing each to the other;     -   drilling holes in the bridge for fastening the spokes of the         wheel.

According to the invention, the method further comprises machining, carried out after the drilling, whereby, at least one median zone of the outer surface of the bridge, which has a transverse width measured perpendicular to the median plane and greater than 4 mm, over the entire circumference of the rim.

The manufacturing method is standardized, that is to say, it is possible to easily manufacture rims of various geometries from the same section, without the need to change the tools provided for the extruding, bending, and machining. For example, for the manufacture of a line of rims, various front and rear wheel rims can be made from the same section and using the same machining tools.

Fatigue cracks generally occur in the area of the bridge of the rim, around the spoke fastening zones. If the strength of a rim made by such a method proves to be insufficient, the thickness of the bridge of the rim can easily be increased, at least in the area of certain zones of the circumference of the rim, by keeping the initial tools and by varying the geometric parameters of the machining. For example, if the rim is machined with a milling cutter having a concave profile, it suffices to shift the milling cutter toward the axis of rotation of the rim to increase the thickness of its walls. Thus, the rim development costs are reduced.

According to advantageous but not essential aspects of the invention, such a manufacturing method may incorporate one or more of the following characteristics, taken in any technically permissible combinations:

-   -   The outer surface of the bridge is machined in its entirety,         over the entire circumference of the rim.     -   During machining, an outer surface of the rim, facing outward of         the rim and including both the outer surface of the bridge and         at least a portion of the outer surface of the sidewalls         connected to the outer surface of the bridge, is machined in its         entirety, over the entire circumference of the rim.     -   Machining is carried out using a milling cutter having a concave         profile and enabling the bridge and at least a portion of the         sidewalls adjoining the bridge to be machined simultaneously in         a radial plane.     -   At the end of extruding, a radius of curvature of the outer         surface of the bridge of the section, measured in a radial plane         of the rim, is greater than 20 mm. At the end of machining, a         radius of curvature of the outer surface of the bridge of the         rim is less than 15 mm or, in particular embodiments, less than         10 mm.     -   At the end of extruding, a thickness of the bridge of the         section is greater than 1.6 mm or, in particular embodiments,         greater than 1.9 mm.     -   A ratio, whose denominator is a thickness of the bridge of the         section, measured at the end of extruding, and whose numerator         is a thickness of the bridge of the rim, measured at the end of         machining, is less than 90%.     -   During drilling, holes and bushings for fastening the spokes are         made simultaneously by flow drilling the bridge, without         cutting.     -   A minimum removed material thickness, equal to the difference         between the thickness of the bridge of the section, measured at         the end of extruding, and the minimum thickness of the bridge of         the rim, measured at the end of machining and considered over         the entire circumference of the rim, is greater than 0.1 mm or,         in particular embodiments, greater than 0.3 mm.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood upon reading the following description of a cycle wheel rim and of a method for manufacturing such a rim in accordance with its principle, given solely by way of example and in reference to the annexed drawings, in which:

FIG. 1 is a perspective view of a cycle wheel shown without the tire and including a rim according to the invention;

FIG. 2 is a side view of the detail II of FIG. 1;

FIGS. 3, 4, and 5 are radial cross sections along the lines III-III, IV-IV, and V-V of FIG. 2, the spokes being omitted in FIG. 5 for clarity of the drawing;

FIG. 6 is a transverse cross section of a section from which the rim is made;

FIG. 7 is a perspective view of an unworn rim brake element, used to brake the wheel of FIG. 1 and shown bearing against the rim, which is partially shown;

FIG. 8 is a cross section along the plane P8 of FIG. 7;

FIG. 9 is a view, similar to FIG. 7, of a worn out rim brake element;

FIG. 10 is a block diagram of a method for manufacturing the rim;

FIG. 11 is a view, similar to FIG. 2, of a rim according to a second embodiment of the invention;

FIGS. 12-15 are cross sections along the lines XII-XII, XIII-XIII, XIV-XIV, and XV-XV of FIG. 11, the spokes being omitted in FIGS. 12, 13, and 15 for clarity of the drawings;

FIG. 16 is a schematic diagram showing two cross sections of a rim according to a third embodiment of the invention, overlaid with a cross section of a section from which this rim is made;

FIG. 17 is a perspective view of a milling cutter used during the manufacture of the rim of FIG. 1;

FIG. 18 is a transverse cross section of a section from which a rim is manufactured according to a fourth embodiment of the invention;

FIG. 19 is a radial cross section of the rim according to the fourth embodiment of the invention;

FIG. 20 is a schematic diagram showing three cross sections of the rim of FIG. 19, overlaid with the cross section of the section of FIG. 18; and

FIG. 21 is a view, on a larger scale, of the detail XXI of FIG. 20.

DETAILED DESCRIPTION

FIG. 1 shows a bicycle rear wheel 1, without a tire mounted thereon. The wheel 1 comprises two sets 4 a, 4 b of spokes 4 a 1, 4 a 2, 4 b 1 mounted on a rim 3. The spoke sets 4 a, 4 b are connected to a hub 2 of the wheel 1, which comprises a hub body 21 extending along an axis of rotation X of the wheel 1. A freewheel mechanism 22 is connected to one end of the hub body 21 which supports the spoke set 4 a, and the other end of the hub body 21 supports the spoke set 4 b. The freewheel mechanism 22 is provided to be assembled with a sprocket cassette (not shown).

When a cyclist pedals in the forward direction, the cyclist rotates the wheel 1 about the axis of rotation X through the sprocket cassette and the freewheel mechanism 22 in a direction designated by the arrow F in FIG. 1.

The spoke set 4 a comprises driving spokes 4 a 2, which pull on the rim 3 when the cyclist pedals, and non-driving spokes 4 a 1, or pushing spokes, which tend to relax when the cyclist pedals. The spoke set 4 a is the driving set; its spokes 4 a 1 and 4 a 2 are fastened on the side of the hub body 21 which carries the freewheel mechanism 22 and receives the torque resulting from the pedaling force from the cyclist. Conversely, the spoke set 4 b is the driven set.

As shown in FIGS. 3 to 5, the radial cross section of the rim 3, is in the form of a hollow box, or having a U-shape, with a transverse wall 7, or bridge, connecting the two vertical arms of the “U”. The expression “radial cross section” refers herein to a cross section in a plane P4 passing through the axis X, oriented along a radial direction. The rim 3 comprises two lateral sidewalls 5 a and 5 b, or sidewalls, and a curved, or arcuate, bridge 6 connecting the sidewalls 5 a and 5 b to one another and forming the curved portion of the U-shaped cross section. The bridge 6 is located on the side of the axis of rotation X, or faces the axis of rotation, and the transverse wall 7 is located on the side of the tire, or faces the tire. Although the transverse wall 7 could be referred to as a bridge or upper bridge (and bridge 6, a lower bridge), the wall 7 is referred to herein as a transverse wall. The rim 3 thus demarcates an inner volume V. The convex side of the bridge 6 is oriented so as to be opposite the axis X, and the concave side of the bridge 6 is oriented toward the tire. The transverse wall 7 is generally perpendicular to the sidewalls 5 a and 5 b and connects the sidewalls 5 a and 5 b to one another, opposite the bridge 6. On the side opposite the bridge 6, the sidewalls 5 a and 5 b are each provided with an L-shaped flange 51 a and 51 b, provided for fastening a tire, not shown, to the rim 3. The flanges 51 a and 51 b project outward of the box formed by the rim 3. The box shape of the rim 3 is demarcated by the sidewalls 5 a and 5 b, the bridge 6, and the transverse wall 7.

The rim 3 is provided to be used with a rim brake system comprising two braking elements 8, one of which is shown in FIG. 7; such braking elements 8 are mounted on a stirrup attached to the frame of the cycle. Each braking element 8 comprises a pad 81 mounted on a support element 82 and extends longitudinally along an axis X8 which, during use, is locally tangent to a circumferential direction of the rim 3. In other words, during use, the axis X8 extends along an orthoradial direction of the rim 3. Each pad has a decreasing width L8, between the portion 84 fixed to the support 82 and the friction surface S8 in the form of a ring section, which comes into contact with braking surfaces S5 a and S5 b of the rim 3 during braking. The width L8 is measured perpendicular to the axis X8 and parallel to the surface S8.

The braking surfaces S5 a and S5 b are defined outside of the volume V by the flanges 51 a and 51 b and a portion of the sidewalls 5 a and 5 b adjoining the flanges 51 a and 51 b. The surfaces S5 a and S5 b are flat and perpendicular to the axis X.

Notable is a median plane P of the wheel 1, perpendicular to the axis X. The median plane P passes between the sidewalls 5 a and 5 b and between the flanges 51 a and 51 b, at equal distances therefrom. Thus, the sidewalls 5 a and 5 b are located on opposite sides of the median plane P.

Also notable is the height h5 of the braking surfaces S5 a and S5 b, measured parallel to the plane P, along a radial direction R of the wheel 1. See FIG. 3.

The peripheral ends of the spokes 4 a 1, 4 a 2, 4 b 1 are equipped with threaded heads 40 attached to the bridge 6 of the rim 3. The bridge 6 comprises holes 41, the edges of which are extended inward of the inner volume V by a generally cylindrical bushing 42. The bushings 42 are internally threaded for threaded engagement with the heads 40.

A valve hole 43 (see FIG. 1) is made through the bridge 6 and the transverse wall 7. When a tire is mounted on the rim 3, the tire valve is inserted into the valve hole 43 and projects outward from the rim 3.

The transverse wall 7 is provided with a locating member 71, such as a ridge, that is offset relative to the plane P. The locating member 71 makes it possible to identify the right side and the left side of the rim 3, to facilitate the mounting of the spokes 4 a 1, 4 a 2, 4 b 1.

The bridge 6 has a thickness e6 measured along the radial direction R, in the plane P and perpendicular to the axis X.

The rim 3 is divided into a plurality of zones Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1, which divide the circumference of the rim 3 into a plurality of angular sectors. The transmission zones Z3 a 1, Z3 a 2, Z3 b 1 are located around holes 41 where the spokes 4 a 1, 4 a 2, 4 b 1 are mounted. Two transition zones Z2 are located on both sides of each transmission zone Z3 a 1, Z3 a 2, Z3 b 1. The intermediate zones Z1 are located between the transition zones Z2 and are farther away from the holes 41 than the zones Z2, Z3 a 1, Z3 a 2, Z3 b 1. Thus, each transition zone Z2 is located between a transmission zone Z3 a 1, Z3 a 2, Z3 b 1 and an intermediate zone Z1.

During use, the transmission zones Z3 a 1, Z3 a 2, Z3 b 1 are subject to mechanical stresses of relatively high intensity because it is in this area that the force produced by the cyclist is transmitted to the rim 3. The transition zones Z2 are subject to mechanical stresses of average intensity because they are adjacent the transmission zones Z3 a 1, Z3 a 2, Z3 b 1. The intermediate zones Z1 are subject to relatively low mechanical stresses because they are away from the transmission zones Z3 a 1, Z3 a 2, Z3 b 1.

The greater the thickness e6 of the bridge 6, the stronger and heavier the rim 3 will be. Conversely, the smaller the thickness e6 of the bridge 6, the weaker and lighter the rim 3 will be. To obtain a rim 3 with satisfactory mechanical strength and reduced weight, the thickness e6 is adapted as a function of the mechanical stresses withstood by the various zones Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1.

In the area of the intermediate zones Z1, the thickness e6 is equal to a minimum thickness of e6. The minimum thickness of e6 is less than 0.8 mm or, in a particular embodiment, less than 0.65 mm.

In the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, the thickness e6 is equal to a maximum thickness of e6, greater than the minimum thickness of e6. The maximum thickness of e6 is greater than 1.6 mm or, in a particular embodiment, greater than 2.0 mm.

Moreover, the intensity of the mechanical forces transmitted to the rim 3 by the spokes 4 a 1, 4 a 2, 4 b 1 is not the same, depending upon whether the spoke 4 a 1, 4 a 2, or 4 b 1 is part of a driving or driven set 4 a or 4 b, and whether the spoke is a driving spoke 4 a 2 or a non-driving spoke 4 a 1. In addition, the intensity of the forces transmitted is not the same for the wheel 1, which is the drive wheel of the cycle, and for the front wheel of the cycle, not shown.

Thus, the maximum thickness of e6 is not the same for each transmission zone Z3 a 1, Z3 a 2, Z3 b 1. The maximum thickness of e6 of the transmission zones Z3 a 1, in which the driving spokes 4 a 2 are fastened, is greater than the maximum thickness of e6 of the transmission zones Z3 a 2, in which the non-driving spokes 4 a 1 are fastened. The maximum thickness of e6 of the transmission zones Z3 b 1, in which the driving spoke set 4 a is fastened, is greater than the maximum thickness of e6 of the transmission zones Z3 a 2, in which the driven spoke set 4 b is attached. The thickness e6 of the drive wheel 1 of the cycle, in a particular embodiment, is greater than or equal to the thickness e6 of the front wheel of the cycle.

Optionally, the sidewalls 5 a and 5 b can be locally thicker in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1 and in the area of the connecting zones Z2 than in the area of the intermediate zones Z1, in order to reduce the risks of rupture for the rim 3.

In the area of the transition zones Z2, the thickness e6 is equal to an intermediate thickness of e6 between the minimum thickness of e6 and the maximum thickness of e6. For each transition zone Z2, the intermediate thickness of e6, in a particular embodiment, varies progressively along the circumference of the rim 3, between the intermediate zone Z1 and the respective transmission zone Z3 a 1, Z3 a 2, Z3 b 1 adjacent the transition zone Z2.

Notable is an outer surface S3 of the rim 3, located outside of the inner volume V and defined by the bridge 6 and by the portions of the sidewalls 5 a and 5 b located between the bridge 6 and the braking surfaces S5 a and S5 b. In the illustrated embodiment, the outer surface S3 is associated, i.e., in one piece, therewith. In the radial plane P4 of the rim 3, noted is the radius of curvature R6 of an outer surface S6 of the bridge 6, which is oriented so as to be opposite the axis of rotation X and is outside of the volume V. The outer surface S6 has a center of curvature C6. The bridge 6 is not exactly in the form of an arc of a circle. Therefore, the radius of curvature R6 is variable. The radius of curvature R6 is measured on a median zone Z6 of the bridge 6, which has a transverse width measured perpendicular to the plane P and equal to 10 mm.

In the median zone Z6, the radius of curvature R6 is less than 15 mm or, in a particular embodiment, less than 10 mm. For example, the radius R6 is equal to 8.0 mm. A large radius of curvature R6 would degrade the aerodynamics of the rim 3. The small radius of curvature R6 provides the rim 3 with optimized aerodynamics.

As shown in FIG. 2, the height h5 of the braking surfaces S5 a, S5 b is greater in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1 than in the area of the intermediate zones Z1. As explained below, this constitutes an audible indicator of worn-out pads 81.

The rectangular zone Z8 of the rim 3, shown in FIG. 2, represents the zone of contact between the surface S8 of the pad 81 and the rim 3 during braking, when the pad 81 is not worn out, or is slightly worn out. This configuration is shown in FIG. 7. Over the entire circumference of the rim 3, the contact between the pad 81 and the rim 3 occurs only in the area of the a respective braking surface S5 a, S5 b, and the friction surface S8 of the pad 81 does not cover the outer surface S3 of the rim 3, which is set back toward the median plane P with respect to each respective braking surface S5 a, S5 b.

The zone Z8′ of the rim 3 represents the contact zone between the friction surface S8 of the pad 81 and the rim 3 during braking, when the pad 81 is worn out. This configuration is shown in FIG. 9. Due to the flared shape of the pad 81, the surface of the zone Z8′ is larger than the surface of the zone Z8. When a pad 81 is worn out and in contact with the rim 3 above the outer surface S3, in the area of the intermediate zones Z1, a portion of the friction surface S8 of the pad 81 overlaps in the area of the braking surfaces S5 a, S5 b. In the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, the contact between the pad 81 and the rim 3 occurs entirely, or almost entirely, on the braking surfaces S5 a, S5 b. Thus, when the pad 81 is worn out, due to the height difference Δh between the intermediate zones Z1 and the transmission zones, Z3 a 1, Z3 a 2, Z3 b 1, the portion of the friction surface S8 of the pads 81 which, during braking, is in contact with the rim 3 in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, is larger than in the area of the intermediate zones Z1.

During braking, the wheel 1 turns and the pad 81 rubs on the braking surfaces S5 a, S5 b. When the pad 81 is not worn out, the sound produced by this friction is constant throughout the braking. Conversely, when the pad 81 is worn out, the sound produced by the friction changes when the pad 81 rubs in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1. This difference in sound enables the user to determine, during braking, whether the pad 81 is worn out. Indeed, due to the height difference Δh, the sound produced by the friction of the pads 81 becomes discontinuous if the pads 81 are worn out, and a staccato sound alerts the user that the pads 81 are worn out.

The width L8 of the pad 81 decreases in a more pronounced manner on the side of the pad 81 turned toward the axis of rotation X and in the vicinity of the support 82 than on the side of the friction surface S8. Due to the sharp variation in the width L8 near the support 82, in the zone of maximum wear of the pad 81, the sound signal is emitted quite suddenly, thereby making it easy to detect. This sharp variation in the width L8 occurs on the side of the axis of rotation X because this zone rubs on the portion of the braking surfaces S5 a, S5 b having the height differences Δh that is useful for the detection of wear. Alternatively, the pad 81 is symmetrical and its width L8 decreases in a more pronounced manner in the vicinity of the support 82, on the side of the pad 82 turned toward the axis of rotation X and on the side of the pad 82 turned toward the tire.

The following description relates to a method for manufacturing the rim 3, shown in FIG. 10, which proceeds successively from 1001 to 1008.

During extrusion 1001, a rectilinear section 30, whose transverse cross section is shown in FIG. 6, is made by extruding or spinning a metal alloy, such as an aluminum alloy, for example. The cross section of the section 30 is similar to that of the rim 3 and comprises two sidewalls 5 a, 5 b and an arcuate bridge connecting the sidewalls 5 a, 5 b. A transverse wall 7, generally perpendicular to the sidewalls 5 a, 5 b, connects the sidewalls 5 a, 5 b to one another. On the side opposite the bridge, the sidewalls 5 a, 5 b are each provided with an L-shaped flange 51 a, 51 b.

The bridge of the section 30 has a thickness e60, shown in FIG. 6, measured along the radial direction R in the median plane P, perpendicular to the longitudinal axis X30 of the section.

The outer surface S60 of the bridge of the section 30 has a center of curvature C0 and a radius of curvature R0, measured over a zone Z60 10 mm wide. The radius R0 is greater than the radius R6 of the rim 3. The radius R0 is greater than 20 mm.

During bending 1002, the portion of the section 30 is bent to form a plurality of circular helical coils, for example by means of a roll bender. For example, three coils are formed from the section 30 which then has a length equivalent to about three times the circumference of the rim 3.

During cutting 1003, the coils are cut to obtain a plurality of rings having the same perimeter as the rim 3.

To avoid the appearance of defects in the material of the section 30 during the extrusion, the walls of the section 30 should be sufficiently thick. In addition, when the walls of the section 30 are too thin, the section 30 may buckle during bending, and undesired bends may form in the area of the bridge during bending. To prevent these conditions, the thickness e60 of the bridge of the section 30 is greater than 1.6 mm or, in a particular embodiment, greater than 1.9 mm.

During assembly 1004, the ends of the ring obtained during the cutting 1003 are butt-joined and affixed to one another, for example by welding. Alternatively, the ends can be connected by sleeving, by inserting an attached element in the inner volume V at respective ones of the ends of the ring.

The thickness e60 of the section 30 is sufficiently great to produce a solid weld. If the thickness e60 is too small, the weld becomes very difficult to achieve and may break.

During drilling 1005, the valve hole 43 is made, for example by means of a drill.

During flow drilling 1006, the holes 41 and bushings 42 for fastening the spokes 4 a 1, 4 a 2, 4 b 1 are made simultaneously by flow drilling, that is to say, by drilling without cutting. To do this, a flow drill bit operating on the outer surface of the bridge, in the direction of the transverse wall 7, is used to create the bushings 42. The initial thickness e60 of the bridge is sufficient for the bushing 42 to have good mechanical strength. Indeed, the quantity of material flowing back is relatively large, which makes it possible to obtain a sufficiently thick bushing. The valve hole 43 forms an angular reference mark for making the holes 41 and the bushings 42, as well as for carrying out the following parts of the method.

The radius R0 is relatively large, which prevents the flow drill bit from slipping on the bridge, especially when a drill bushing is not used to hold it.

During machining 1007, the outer surface S3 of the rim 3 is machined in its entirety over the entire periphery of the rim 3, that is to say, over 360° and over each zone Z1, Z2, Z3 a 1, Z3 a 2, and Z3 b 1. For example, one can use a concave milling cutter 100, shown in FIG. 17, which has a generally U-shaped profile or cutting surface and which rotates in the direction F100 about axis X100, and which makes it possible to machine the entire outer surface S3 in a single pass, concurrently in the area of the bridge and in the area of the sidewalls 5 a, 5 b. Alternatively, a convex milling cutter, a round bur, or any other appropriate cutting tool, can be used.

During a complementary machining portion of the method, the braking surfaces S5 a and S5 b are machined, for example by means of an end mill.

Thus, the only machined surfaces of the rim 3 are the outer surface S3 and the braking surfaces S5 a and S5 b. The inner surface S7 a of the transverse wall 7, which demarcates the volume V, as well as surfaces S′6 a, S′5 a, S′5 b of the bridge and of the sidewalls 5 a, 5 b which demarcate the volume V, are not machined. Similarly, the outer surface S7 b of the transverse wall 7, which is located outside of the volume V and includes the locating member 71, is not machined. In other words, the only surface of the rim 3 which is machined is an “extended” outer surface that includes the outer surface S3 and the braking surfaces S5 a and S5 b.

In the case in which the ends of the section 30 are welded together, the machining 1007 makes it possible to trim the weld and create a smooth surface finish over the entire circumference of the rim 3. The weld is then no longer visible, thereby improving the aesthetics of the rim 3. It is not necessary to machine the weld seam subsequently, thus reducing the number of manufacturing steps.

When the rim 3 is machined with a concave milling cutter, the curvature of the outer surface S3 is continuous and does not form a ridge. In other words, the trace of the outer surface S3 in a radial plane is a curve whose derivative is continuous. Therefore, the aerodynamics of the wheel are improved.

The machining is relatively simple as it can be carried out with a single-axis milling machine, by rotating the rim 3 about the axis X in relation to the tool and by radially translating the tool, which simultaneously creates the variations in the thickness e6 of the zones Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1 and the variations in the height h5. This makes it possible to reduce the cycle time to less than 1 minute. Thus, the manufacturing cost of the rim 3 is reduced.

Because flow drilling is performed prior to machining, the trimming of the holes 41 and 43 occurs automatically during the machining 1007. It is not necessary to perform additional trimming for the holes 41 and 43.

In threading 1008, the inner surface of each of the bushings 42 is threaded to form a thread for threaded engagement of the heads 40 of the spokes 4 a 1, 4 a 2, 4 b 1.

During machining, the removed material thickness in the area of the bridge is more or less substantial, depending upon the machined zone Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1. The transmission zones Z3 a 1, Z3 a 2, Z3 b 1 retain a relatively substantial maximum thickness of e6. Between the spokes, the thickness of e6 of the intermediate zones Z1 is finer. The transition zones Z2 have an intermediate thickness of e6 that varies progressively.

The machined material thickness and the location of the holes 41 may be adjusted according to several parameters, such as the number of spokes of the wheel 1, the weight of the user, the type of brake (shoe or disk brake), the type of practice (track biking, cross biking, mountain biking, etc.), and the type of spokes, for example. Thus, a rim adapted to the desired application can be made from the same section 30 by changing the manufacturing parameters, in particular the machining range.

In a supplemental machining portion 1009 of the method, the braking surfaces S5 a and S5 b are machined, for example, by turning or with an end mill.

Notable is a ratio A, whose denominator is the thickness e60, and whose numerator is the maximum thickness of e6. The ratio A is less than 90%.

In the embodiment mentioned above, for example, the ratio A is equal to 87.5% (2.1/2.4).

Alternatively, the variation of the thickness e6 between the minimum thickness of e6 and the maximum thickness of e6 is not progressive, such that the outer surface S3 of the rim 3 has, at least in the area of the bridge, a ridge or break that is generally oriented parallel to the axis X. In this case, in the area of the transition zones Z2, the intermediate thickness of e6 has a discontinuous variation along the circumference of the rim 3, between the intermediate zone Z1 and the transmission zone Z3 a 1, Z3 a 2, and Z3 b 1 adjacent the transition zone Z2.

The rim 3 is part of a rear cycle wheel 1, but the invention also applies to front wheels. The invention also applies to rims having varied numbers of spokes and of various types.

Alternatively, during the flow drilling 1006, boring with material removal is used, instead of flow drilling. In such a case, the rim is cut out to form the holes 41. Bushes can then be fixed in the holes 41 for fastening the spokes 4 a 1, 4 a 2, 4 b to the rim 3. Flow drilling, which consists of drilling without material removal, and drilling with material removal, are considered two alternative methods of drilling.

The milling cutter 100 shown in FIG. 17 has a concave profile with a continuous curvature. In an alternative, however, the concave profile has at least one ridge oriented along a circumferential direction, for example between the bridge and a sidewall 5 a or 5 b.

FIGS. 11 to 15 show a rim 103 according to a second embodiment of the invention. In the second embodiment, the elements similar to those of the first embodiment are not described in detail. The elements of the rim 103 similar to those of the rim 3 are designated by the same reference numerals increased by 100.

The rim 103 is made from an asymmetrical section to improve the distribution of the forces transmitted between the rim 103 and the spokes 4 a 1, 4 a 2, 4 b 1, which do not extend exactly along the radial direction R and do not all have the same orientation in relation to the plane P.

The rim 103 is made using a method similar to that described above. It is possible to machine the rim 103 from an asymmetrical section, with a milling cutter having a concave profile, whose axis of rotation is inclined relative to the plane P.

The transverse cross section of the rim 103 has the shape of a hollow box and comprises two sidewalls 105 a, 105 b and a bridge 106. A transverse wall 107 connects the sidewalls 105 a, 105 b to one another, opposite the bridge 106. On the side opposite the bridge 106, the sidewalls 105 a, 105 b are each provided with an L-shaped flange 151 a, 151 b, provided for fastening a tire, not shown, to the rim 103.

Holes 141 connected to bushings 142 are made in the bridge 106.

Similar to the rim 3, the rim 103 is divided into a plurality of zones Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1, which divide the circumference of the rim 103 into a plurality of angular sectors. As shown in FIGS. 12 to 15, the thickness of the bridge 106 varies, depending upon the zone Z1, Z2, Z3 a 1, Z3 a 2, Z3 b 1 of the rim 103, in a manner similar to the rim 3 of the first embodiment.

The thickness of the bridge varies between a maximum thickness e106max, in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 b 1, and a minimum thickness e106min in the area of the intermediate zones Z1. In the area of the transition zones Z2, the thickness of the bridge is equal to an intermediate thickness between the minimum thickness e106min and the maximum thickness e106max.

The maximum thickness e106max of the bridge in the transmission zones Z3 a 1 of the driving spokes 4 a 2 is greater than the maximum thickness e106max of the bridge in the transmission zones Z3 a 2 of the non-driving spokes 4 a 1. The maximum thickness e106max of the bridge in the transmission zones Z3 b 1 at the spokes 4 b 1 of the driven spoke set 4 b is less than the maximum thickness e106max of the bridge at the spokes 4 a 1, 4 a 2 of the driving spoke set 4 a.

FIG. 16 shows a rim 203 according to a third embodiment of the invention. In the third embodiment, the elements similar to those of the first embodiment are not described in detail. The elements of the rim 203 similar to those of the rim 3 are designated by the same reference numerals increased by 200.

The rim 203 is made using a method similar to that described above and differs from the rims 3 and 103 in that it is part of a disc brake wheel.

The transverse cross section of the rim 203 has the shape of a hollow box and comprises two sidewalls 205 a, 205 b and a bridge 206. A transverse wall 207 connects the sidewalls 205 a, 205 b to one another, opposite the bridge 206. On the side opposite the bridge 206, the sidewalls 205 a, 205 b are each provided with an L-shaped flange 251 a, 251 b, provided for fastening a tire, not shown, to the rim 203.

The rim 203 has an outer surface S203, which is oriented outward of the rim 203 and is defined by the bridge 206 and by the sidewalls 205 a, 205 b, up to the free ends of the flanges 251 a, 251 b. In radial cross section, the outer surface S203 is curved over its entire length. Unlike the rims 3 and 103, the outer surface S203 does not include a planar zone provided to cooperate with a brake pad.

In FIG. 16, a hatched zone M1 corresponds to the transverse cross section of the rim 203, in the area of the intermediate zones Z1 in which the thickness of the bridge 206 is equal to a minimum thickness e206min of the bridge.

The joining of the hatched zone M1 with a hatched zone M2 corresponds to the transverse cross section of the rim 203, in the area of the transmission zones Z3 a 1, Z3 a 2, or Z3 a 3. The maximum thickness e206max of the bridge is measured in the area of the transmission zones Z3 a 1, Z3 a 2, Z3 a 3, on the joining of the zones M1 and M2. The hatched zone M2 corresponds to the excess material thickness between the intermediate zones Z1 and the transmission zones Z3 a 1, Z3 a 2, or Z3 a 3 and represents the difference between the minimum thickness e206min of the bridge and the maximum thickness e206max of the bridge.

The joining of the hatched zones M1 and M2 with a hatched zone M3 corresponds to the transverse cross section of a section 230 from which the rim 203 is manufactured. Notable is the thickness e260 of the bridge 206 of the section 230. The thickness e260 is greater than the maximum thickness e206max of the bridge.

The following description provides examples of various thicknesses of the rim 203 and of the section 230. These thicknesses can also be selected for the rims 3 and 103.

The thickness e260 of the bridge 206 of the non-machined section 230, measured at the end of the extrusion 1001 and prior to the bending 1002, is equal to 2.5 mm.

At the end of machining 1007, the maximum thickness of e206max of the bridge, measured in the area of the transmission zones Z3 a 2 in which the driving spokes 4 a 2 are fastened, is equal to 2.1 mm. These transmission zones Z3 a 2 are the most mechanically biased in view of the fastening of the driving spokes 4 a 2. Considering the rim 203 at the end of its manufacture, the thickness of the bridge in the area of the transmission zones Z3 a 2 is the greatest thickness of the bridge 206 over the entire circumference of the rim 203.

The maximum thickness e206max of the bridge, measured in the area of the transmission zones Z3 a 1 in which the non-driving spokes 4 a 1 are fastened, is equal to 1.9 mm.

The maximum thickness e206max of the bridge, measured in the area of the transmission zones Z3 b 1 in which the spokes 4 b 1 of the driven spoke set 4 b are fastened, is equal to 1.7 mm. The spokes 4 b 1, located opposite the free wheel mechanism 22 of the hub 2, do not transmit torque and thus are not very biased, which explains the relatively small value of the thickness of the bridge in the zones Z3 b 1.

In the area of the intermediate zones Z1, the minimum thickness of the bridge is equal to 0.65 mm.

In this example, the greatest difference between the maximum thickness e206max of the bridge and the minimum thickness e206min of the bridge, considered in the area of the transmission zones Z3 a 2 of the driving spokes 4 a 2, is equal to 1.25 mm.

ε206 is the removed material thickness at the bridge 206, at the end of the machining 1007, measured along the radial direction R, in the plane P and perpendicular to the axis X. The thickness ε206 is equal to the difference between the thickness e260 of the bridge 206 of the section 230 and the thickness of the bridge 206 of the rim 203. The removed material thickness ε206 varies as a function of the zone Z3 a 1, Z3 a 2, Z3 b 1, Z2, or Z1 considered. The maximum removed material thickness ε206max is reached in the area of the intermediate zones Z1, in which it is equal to 1.45 mm. The minimum removed material thickness ε206min of ε206 is reached in the area of the transmission zones E3 a 2 of the driving spokes 4 a 2, in which it is equal to 0.2 mm.

During the machining 1007, the minimum removed material thickness ε206min of ε206 selected must be sufficiently substantial in order for the machining to eliminate the asperities generated during the extrusion and bending of the section 230. In a particular embodiment, the minimum removed material thickness ε206min of ε206 is greater than 0.1 mm or, in specific case, greater than 0.3 mm.

In addition, during the machining 1007, the depth-of-cut selected should be sufficiently small to ensure complete continuity of the cut and to guarantee a smooth surface finish. In one embodiment, the cutting depth can be less than 0.4 mm; in another embodiment, a cutting depth of less than 0.2 mm can be selected.

FIGS. 18-21 show a rim 303 and a section 330 consistent with a fourth embodiment of the invention and forming part of a disc brake wheel. In the fourth embodiment, the elements similar to those of the first embodiment are not described in detail. The elements of the rim 303 and of the section 330 similar to those of the rim 3 and of the section 30 according to the first embodiment are designated by the same reference numerals increased by 300.

The transverse cross section of the rim 303 has the shape of a hollow box and comprises two lateral sidewalls 305 a and 305 b and a bridge 306. A transverse wall 307 connects the sidewalls 305 a, 305 b to one another, opposite the bridge 306. On the side opposite the bridge 306, the sidewalls 305 a, 305 b are each provided with an L-shaped flange 351 a, 351 b, provided for fastening a tire, not shown, to the rim 303.

The rim 303 is made using a method that is generally similar to that described above and differs from the rims 3, 103, and 203 in that only the bridge 306 of the rim 303 is machined during the machining 1007. Thus, the lateral sidewalls 305 a, 305 b are not machined.

The rim 303 has an outer surface S303 oriented outward of the rim 303 and defined by the bridge 303 and by all of the sidewalls 351 a, 351 b, up to the free end of the flanges 251 a, 351 b.

In FIGS. 20 and 21, a hatched zone M10 corresponds to the transverse cross section of the rim 303, in the area of the intermediate zones Z1, in which the thickness of the bridge 306 is equal to a minimum thickness e306min of the bridge.

The joining of the hatched zone M10 with a hatched zone M20 corresponds to the transverse cross section of the rim 303, in the area of the transmission zones Z3 b 1 in which the spokes 4 b 1 comprised in the driven spoke set 4 b are fastened. Notable is a maximum thickness e′306max measured in the area of the transmission zones Z3 b 1, on the joining of the zones M10 and M20. The hatched zone M20 thus corresponds to the excess material thickness between the intermediate zones Z1 and the transmission zones Z3 b 1 and represents the difference between the minimum thickness e306min and the maximum thickness e′306max.

The joining of the hatched zones M10 and M20 with a hatched zone M30 corresponds to the transverse cross section of the rim 303, in the area of the transmission zones Z3 a 1, Z3 a 2, in which the spokes 4 a 1, 4 a 2 comprised in the driving spoke set 4 a are fastened. Notable is a maximum thickness e306max measured in the area of the transmission zones Z3 a 1, Z3 a 2, on the joining of the zones M10, M20, and M30. The hatched zone M30 thus corresponds to the excess material thickness between the transmission zones Z3 b 1 in which the spokes 4 b 1 of the driven spoke set 4 b are fastened and the transmission zones Z3 a 1, Z3 a 2 in which the spokes 4 a 1, 4 a 2 of the driving spoke set 4 a are fastened. The hatched zone M30 thus represents the difference between the maximum thickness e′306max and the maximum thickness e306max.

The joining of the hatched zones M10, M20, M30, with a hatched zone M40 corresponds to the transverse cross section of the section 330 from which the rim 303 is made. Notable is the thickness e360 of the bridge 306 of the section 330. The thickness e360 is greater than the maximum thickness e306max.

The thicknesses of the rim 303 and of the section 330 may be selected to be equal to the thicknesses of the rim 203 and of the section 230 according to the third embodiment.

The following description relates to a fifth embodiment of the invention, in which a rim, not shown, is made from the section 330 of FIG. 18.

The method for manufacturing this rim is generally similar to that for the rim 303. However, in the machining 1007, only a median zone Z306 of the outer surface of the bridge 306 is machined, over the entire circumference of the rim. Thus, the bridge 306 is not machined in its entirety. The median zone Z306 has a transverse width L306, measured perpendicular to the median plane P and greater than or equal to 4 mm. Thus, the bridge 306 is machined in the vicinity of all of the zones of attachment of the spokes 4 a 1, 4 a 2, 4 b 1, in the locations in which the mechanical stresses are the most substantial. Machining the bridge 306 only in the area of the median zone Z6 delays the appearance of cracks that might be initiated when the rim is used and subject to conditions causing fatigue. For example, it is possible to machine the intermediate zones Z1 only, or both the intermediate zones Z1 and the transition zones Z2.

The known prior art methods for manufacturing rims have systematically sought to reduce the thickness of the section to a maximum. By contrast, the invention deliberately provides a thickness e60 of the bridge 6 of the section that is relatively substantial, greater than the maximum thickness of e6 of the bridge 6, considered at the end of the manufacture of the rim 3 and over the entire circumference of the rim 3, and to subsequently machine the entire circumference of the rim 3.

In the context of the invention, the various embodiments described above can be combined with one another, at least partially.

At least because the invention is disclosed herein in a manner that enables one to make and use it, by virtue of the disclosure of particular exemplary embodiments of the invention, the invention can be practiced in the absence of any additional element or additional structure that is not specifically disclosed herein. 

The invention claimed is:
 1. A rim for a cycle wheel, said rim comprising: two lateral sidewalls located on opposite respective sides of a median plane of the rim and each of the two lateral sidewalls comprising an outer surface facing away from the median plane; a bridge connecting the sidewalls to one another and comprising an outer surface facing an axis of rotation of the wheel; the two lateral sidewalls and the bridge forming a U-shaped radial cross section; the outer surface of the bridge comprising a machined median zone of the outer surface of the bridge extending along an entirety of a circumference of the rim; and the machined median zone having a transverse width, measured perpendicular to the median plane, greater than 4 mm.
 2. A rim according to claim 1, wherein: an entirety of the outer surface of the bridge is a machined outer surface over the entirety of the circumference of the rim.
 3. A rim according to claim 2, further comprising: a rim outer surface comprising both the outer surface of the bridge and at least respective portions of the outer surfaces of the sidewalls; the respective portions of the outer surfaces of the sidewalls being connected to the outer surface of the bridge; the rim outer surface being a machined outer surface over an entirety of the rim outer surface and over the entirety of the rim.
 4. A rim according to claim 3, wherein: the rim outer surface includes an entirety of the outer surfaces of the sidewalls.
 5. A rim according to claim 1, wherein: the rim comprises a plurality of zones dividing the circumference of the rim into angular sectors, the zones comprising: transmission zones located circumferentially at zones of attachment of the spokes of the wheel; and intermediate zones located circumferentially between respective pairs of the transmission zones; in an area of the transmission zones, the bridge having a thickness, measured in the median plane, equal to a maximum thickness; in an area of the intermediate zones, the bridge having a thickness equal to a minimum thickness less than the maximum thickness.
 6. A rim according to claim 5, wherein: the maximum thickness of the bridge is greater than 1.6 mm.
 7. A rim according to claim 5, wherein: the maximum thickness of the bridge is greater than 2.0 mm.
 8. A rim according to claim 5, wherein: the minimum thickness of the bridge is less than 0.8 mm.
 9. A rim according to claim 5, wherein: the minimum thickness of the bridge is less than 0.65 mm.
 10. A rim according to claim 5, wherein: the plurality of zones further includes transition zones each located between a transmission zone and an intermediate zone; in an area of the transition zones, the thickness of the bridge is equal to an intermediate thickness which varies progressively between the minimum thickness and the maximum thickness of the bridge.
 11. A rim according to claim 1, wherein: in a radial cross section of the rim, a radius of curvature of the bridge is less than 15 mm.
 12. A rim according to claim 1, wherein: in a radial cross section of the rim, a radius of curvature of the bridge is less than 10 mm.
 13. A rim according to claim 1, wherein: the bridge comprises internally threaded cylindrical bushings for fastening spokes of the wheel; the bushings are made unitary with the rim.
 14. A rim according to claim 5, wherein: the sidewalls each define a planar braking surface, structured and arranged to cooperate with a brake pad; a height of at least one of the braking surfaces, measured radially, is greater in the area of the transmission zones than in the area of the intermediate zones.
 15. A wheel comprising: a rim; a hub; a plurality of spokes extending between the rim and the hub; the rim comprising: two lateral sidewalls located on opposite respective sides of a median plane of the rim and each of the two lateral sidewalls comprising an outer surface facing away from the median plane; a bridge connecting the sidewalls to one another and comprising an outer surface facing an axis of rotation of the wheel; the two lateral sidewalls and the bridge forming a U-shaped radial cross section; the outer surface of the bridge comprising a machined median zone of the outer surface of the bridge extending along an entirety of a circumference of the rim; and the machined median zone having a transverse width, measured perpendicular to the median plane, greater than 4 mm.
 16. A method for manufacturing a rim for a cycle wheel according to claim 1, the method comprising: extruding a rectilinear section, the section comprising: two lateral sidewalls located on respective opposite sides of the median plane of the rim; the bridge connecting the sidewalls to one another; bending the section to form at least one hoop having two ends; assembling the ends of the hoop of the section to one another to define a circumference; drilling holes through the bridge for fastening the spokes of the wheel; after the drilling, machining at least one median zone of the outer surface of the bridge over an entirety of the circumference of the rim, the median zone having a transverse width of greater than 4 mm measured perpendicular to the median plane of the rim.
 17. A method according to claim 16, wherein: said machining comprises machining the outer surface of the bridge in its entirety over an entirety of the circumference of the rim.
 18. A method according to claim 16, wherein: during said machining, machining an entirety of a rim outer surface over the entirety of the circumference of the rim, the rim outer surface facing outward of the rim and comprising: the outer surface of the bridge; and at least respective portions of the outer surfaces of the sidewalls connected to the outer surface of the bridge.
 19. A method according to claim 18, wherein: said machining comprises machining using of a milling cutter having a concave profile and enabling the bridge and at least the respective portions of the sidewalls adjoining the bridge to be machined simultaneously in a radial plane.
 20. A method according to claim 16, wherein: at the end of said extruding, a radius of curvature of the outer surface of the bridge of the section, measured in a radial plane of the rim, is greater than 20 mm; and at the end said machining, a radius of curvature of the outer surface of the bridge of the rim is less than 15 mm.
 21. A method according to claim 16, wherein: at the end of said extruding, a radius of curvature of the outer surface of the bridge of the section, measured in a radial plane of the rim, is greater than 20 mm; and at the end said machining, a radius of curvature of the outer surface of the bridge of the rim is less than 10 mm.
 22. A method according to claim 16, wherein: at the end of said extruding, a thickness of the bridge of the section is greater than 1.6 mm.
 23. A method according to claim 16, wherein: at the end of said extruding, a thickness of the bridge of the section is greater than 1.9 mm.
 24. A method according to claim 16, wherein: a ratio is less than 90%, said ratio comprising: a denominator being a thickness of the bridge of the section at the end of said extruding; and a numerator being a thickness of the bridge of the rim at the end of said machining.
 25. A method according to claim 16, wherein: during said drilling, holes and bushings for fastening the spokes are made simultaneously by flow drilling the bridge without cutting.
 26. A method according to claim 16, wherein: a machining minimum thickness, equal to the difference between the thickness of the bridge of the section, measured at the end of said extruding, and the minimum thickness of the bridge of the rim, measured at the end of said machining and considered over an entirety of the circumference of the rim, is greater than 0.1 mm.
 27. A method according to claim 16, wherein: a machining minimum thickness, equal to the difference between the thickness of the bridge of the section, measured at the end of said extruding, and the minimum thickness of the bridge of the rim, measured at the end of said machining and considered over an entirety of the circumference of the rim, is greater than 0.3 mm.
 28. A rim for a cycle wheel, said rim comprising: two lateral sidewalls located on opposite respective sides of a median plane of the rim and each of the two lateral sidewalls comprising an outer surface facing away from the median plane; a bridge connecting the sidewalls to one another and comprising an outer surface facing an axis of rotation of the wheel; the two lateral sidewalls and the bridge forming a U-shaped radial cross section; a circumference of the rim being divided into a plurality of circumferentially extending angular sectors, the sectors comprising: a plurality of circumferentially spaced-apart transmission zones, each of the plurality of transmission zones designed to be attached to a respective one of a plurality of spokes of the cycle wheel; a plurality of circumferentially spaced-apart intermediate zones, each of the plurality of intermediate zones being located circumferentially between respective pairs of the transmission zones; the outer surface of the bridge comprising a machined median surface extending circumferentially along at least a radially innermost surface of the plurality of transmission zones and extending circumferentially along at least 95% of an entirety of the circumference of the rim; the machined median surface having a transverse width, measured perpendicular to the median plane, greater than 4 mm; in the plurality of transmission zones, the bridge having a thickness, measured in the median plane, equal to a maximum bridge thickness; and in an area of the intermediate zones, the bridge having a thickness equal to a minimum bridge thickness less than the maximum thickness.
 29. A rim according to claim 28, in combination with the following: a hub and a plurality of spokes extending between the rim and the hub. 